Method of making electron gun mount



Jim. W, 1%? T. J. KELLY 3,293,033

7 METHOD O1T1 MAKING ELECTRON GUN MOUNT Filed Jan. 2, 1964 INVENTOR. THOMAS J. KELLY QM LUJJA AGENT United States Patent 3,298,083 METHOD OF MAKING ELECTRON GUN MOUNT Thomas J. Kelly, West Orange, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Jan. 2, 1964, Ser. No. 335,337 Claims. (Cl. 29-2516) This invention relates to electron tubes and particularly to a novel electron gun mount for an electron tube and method of making the same.

In electron guns for beam tubes, such as traveling wave tubes and klystrons, requiring a cathode and one or more focusing and/or accelerating electrodes, the various electrodes are sometimes mounted in insulated relation by positioning them, or supporting portions thereof, alternately with ceramic insulators to form a multi-sandwich stack. The stack is clamped together by bolts to main tain the parts rigidly assembled together, and suitably mounted in the electron tube. It has been found that electrodes thus mounted in stacks at room temperature become loose in the stack when the tube is operated at high temperatures, as in tubes used in space satellites, or otherwise subjected to high temperature, as during processing b akeout. Springs or compression gaskets have been used to solve this problem but such have not proved entirely satisfactory, particularly at temperature above 500 C.

An object of the present invention is to provide an electron gun mount comprising alternate electrodes and insulators in which the parts are maintained rigidly assembled together at temperatures at least up to 600 C.

Another object is to provide a novel method of making an electron gun mount.

In accordance with the invention, the mounting portions of a plurality of electrodes are sandwiched alternately with insulating spacer members to form a stack, a flanged metal clamp member, having a thermal coeflicient of evzpansion substantially higher than the insulating spacer members, is extended along the stack with its flange engaging one end of the stack, the assembly is heated to a temperature substantially higher than the highest operating temperature to which the structure will be subjected during use, causing the metal clamp member to expand thermally substantially more than the insulating spacer members, the stack is held under compression, and a second flange in engagement with the other end of the stack is formed on or attached to the metal clamp memher while the stack is under compression at its heated temperature, whereby the stack is maintained under compression at lower temperatures, including the operating temperatures, resulting from the different contraction of the insulating spacer members and the metal clamp member on cooling.

In the appended drawing,

FIG. 1 is an axial sectional view, taken on line 1-1 of FIG. 2, of an electron gun structure and apparatus for the assembly there-of according to the invention;

FIG. 2 is a plan view of the upper end of FIG. 1 with the ceramic weight and mounting jig removed; and

FIG. 3 is fragmentary axial sectional view of the cathode mounting member of FIG. 1 with the cathode mounted therein.

The electron gun structure chosen for illustration of the invention in the drawing comprises a cathode mounting member 1, a focusing electrode 3, and an accelerating electrode 5, having respectively central apertures 7, 9 and 11 and radially extending mounting portions 13, and 17, respectively. The cathode 2 and heater 4 (see FIG. 3) are mounted in the aperture 7 of mounting member 1 after the members 1, 3 and 5 are assembled with their respective insulators.

Members 1, 3 and 5 are mounted with their mounting portions 13, 15 and 17 alternating with three insulating rings 19, 21 and 23 in a stack which is maintained under compression by three metal rods 25, to each of which are brazed two metal eyelets or flanges 27 and 29 engaging opposite ends of the stack. Members 1, 3, and 5 may be spider-shaped as shown best in FIG. 2. The rods 25 extend loosely through openings 31 in the spacer rings 19, 21 and 23 and serve as a lead-in for the electrode 5. The cathode spacer ring 19 may be metallized on its outer surface and brazed to a gun support sleeve 33 adapted to be mounted in the electron tube: envelope (not shown).

The gun elements are assembled in the following manner. A metal jig 35, comprising a massive base 37 having three apertures 39 and an upstanding alignment post 41 having three coaxial portions 43, 4.5 and 47 of diflferent diameters snugly fitting the apertures 7, 9, and 11, is positioned on a horizontal suppoiting surface (not shown). The three lower flanges 27 are brazed to the three rods 25 at predetermined points spaced from the lower ends, as shown, at a temperature substantially higher than the subsequent brazing temperature of the upper flanges 29. For example, the lower flanges 27 may be brazed with copper, which has a melting point of about 1080 C., at 1100 to 1120 C.

The three rods 25 are inserted in the holes 39 of base with the flanges 27 abutting the base, and the insulating rings 19, 21 and 23 and portions 13, 15 and 17 are alternately assembled onto the three rods, with the apertures 7, 9 and 11 centered by the portions 43, 45 and 47, respectively, of post 41. The three upper flanges 29 are placed over the rods 25 and on the uppermost electrode 5, and brazing rings 49 are positioned on the rods and flanges. Then a weight 51, preferably of ceramic, having clearance recesses 53 and 55, is placed on the flanges 29 to press the parts together, and the assembly is heated in a furnace (not shown) to a temperature above the melting point of the brazing rings, but below the melting point of the material used to braze the lower flanges 27, to melt the brazing rings and braze the flanges 29 to the rods 25 while the stack is maintained under compression by the weight 51.

For example, if copper is used for the other braze, the rings 49 may be made of a brazing alloy known as Wesgo, having a composition of copper and 35% gold and a melting point of about 980 C., in which case the final furnace temperature should be 1000-1020" C., or about 20-40 above the melting point of the alloy used. Other brazing alloys may be used having lower or somewhat higher melting points. Examples of lower melting point alloys are BT brazing alloy, having a composition of 72% silver and 28% copper and a melting point of about 780 C., and a gold-nickel eutectic having a composition of 82.5% gold and 17.5% nickel and a melting point of about 950 C. Under closely controlled temperature conditions, the rings 49 may be of pure gold having a melting temperature of about 1063 C. or about 17 below that of the copper used for the other braze.

Preferably, the insulating rings 19, 21 and 23 are made of a high alumina ceramic (e.g., 93% A1 0 and the rods 25 are of stainless steel. The ceramic has a thermal coeflicient of expansion of about .9 10- inch/inch/degree C., and the stainless steel has a coeflicient of about 19 10 iuch/inch/degree C. Thus, the differential contraction of the ceramic rings and steel rods on cooling from the final furnace temperature down to room temperature (e.g., 25 C.) places the rings under compressive strain and the rods under tensile strain. Moreover, this strain is not relieved on re-heating the assembly during use up to temperatures approaching the original assem- -bly temperature. If the flanges 29 are brazed at 800 (3 C., the rods will maintain the parts rigidly assembled together at temperatures at least up to 600 C.

Preferably, the cathode mounting member 1 and gun sleeve 33 are of Kovar, and the electrodes 3 and 5 and jig 35 are of molybdenum. The flanges or eyelets 27 and 29 may be of Nichrome V, for example.

In the example shown in the drawing, the inner diameter of the insulating rings is .60", the distance between flanges 27 and 29 is .67", the diameter of rods 25 is .040, the rods are located 120 apart on a circle of .75" diameter, and the apertures in the insulating rings are .060" in diameter. The cathode diameter is .25" and the beam diameter, after focusing, is about 35 mils.

Preferably, lead-in pins or rods 57 and 59 for members 1 and 3, respectively, are mounted in holes 61 in the base 37 at the same time that rods 25 are installed. These pins 57 and 59 extend loosely through apertures 63 in rings 19 and 21 and snugly through apertures in the mounting portions of support number 1 and electrode 3. Brazing rings 67, similar to rings 49, are placed on pins 57 and 59 and mounting portions 13 and 15, so that the pins will be brazed to the mounting portions when the flanges 29 are brazed to the rods 25. Spacer sleeves 69, e.g., of Nichrome V which is 80% nickel and 20% chromium, may be supplied to center the pins 57 and 59 in the insulating rings 19 and 21.

I claim:

1. A method of making an electron gun mount comprising a plurality of axially aligned apertured electrodes having mounting portions alternating with insulating spacer numbers, comprising the steps of:

(a) assembling said electrode in axially aligned relation with said mounting portions alternating with said spacer members in a stack;

(b) extending a flanged emetal member along said stack with the flange thereof engaging one end of the stack, said metal member having a thermal coeflicient of expansion substantially higher than said insulating members;

(c) positioning a second metal flange in engagement with the other end of said stack;

((1) heating the assembly to a temperature of at least 800 C., to cause said metal member to expand thermally substantially more than said stack, and then attaching said second flange to said metal member at said temperature while exerting pressure on said stack through said flanges.

2. The method of making an electron gun mount comprising a plurality of axially aligned apertured electrodes having mounting portions alternating with ceramic spacer rings, comprising the steps of (a) assembling said electrodes in axially aligned relation with said mounting portions alternating with said spacer rings in a stack;

(b) extending a plurality of flanged metal rods through aligned apertures in said mounting portions and spacer rings with the fiange of each rod engaging one end of the stack, said metal rods having a thermal coefli cient of expansion substantially higher than said ceramic rings;

(0) positioning a second metal flange on each rod in engagement with the other end of said stack;

1000 C., to cause said metal rods to expand thermally substantially more than said stack, and attaching said second flanges to said rods at said temperature while exerting pressure on said stack through said flanges.

3. The method as in claim 2, wherein:

(a) said spacer rings are of a high alumina ceramic having a thermal coefli-cient of about 9 10 inch per inch per degree C.; and

(b) said metal rods are of stainless steel having a thermal coeflicient of expansion of about 19 10 inch per inch per degree C.

4. The method of making an electron gun mount com prising a plurality of axially aligned apertured electrodes having mounting portions alternating with ceramic spacer rings, comprising the steps of (a) assembling said electrodes in axially aligned relation with said mounting portions alternating with said spacer rings in a stack;

(b) brazing a flange to one end of each of a plurality of metal rods at a temperature substantially above 1000 C. and extending said rods through aligned apertures in said stack with said flanges engaging one end of the stack, said metal rods having a thermal coeflicient of expansion substantially higher than said ceramic spacer rings;

(c) positioning a second metal flange on each rod in engagement with the other end of said stack;

(d) positioning a brazing ring of a material which melts at a temperature of about 1000 C. adjacent to each rod and associated flange;

(e) heating the assembly to said second named temperature to melt said brazing ring and attach said second flanges to said rods while exerting pressure on said stack through said flanges.

5. The method as in claim 4, wherein:

(a) said spacer rings are of a high almuina ceramic having a thermal coefficient of about 9 10 inch per inch per degree C.;

(b) said metal rods are of stainless steel having a thermal coefficient of expansion of about 19 10 inch per inch per degree C.;

(c) said first named flanges are brazed with copper at about 1120" C.;

((1) said brazing rings are of an alloy containing copper and 35% gold.

References Cited by the Examiner UNITED STATES PATENTS 2,006,081 6/1935 Anderson 2925.l4 X 2,012,689 8/1935 McFarlin 313-250 X 2,212,556 8/1940 Baier 2925.l3 2,348,216 5/ 1944 Holshouser 313250 2,581,446 l/ 1952 Robinson 313250 2,740,186 4/1956 Gates 2925.l3

JOHN F. CAMPBELL, Primary Examiner.

DAVID J. GALVIN, WILLIAM I. BROOKS,

Examiners. 

1. A METHOD OF MAKING AN ELECTRON GUN MOUNT COMPRISING A PLURALITY OF AXIALLY ALIGNED APERTURED ELECTRODES HAVING MOUNTING PORTIONS ALTERNATING WITH INSULATING SPACER NUMBERS, COMPRISING THE STEPS OF: (A) ASSEMBLING SAID ELECTRODE IN AXIALLY ALIGNED RELATION WITH SAID MOUNTING PORTIONS ALTERNATING WITH SAID SPACER MEMBERS IN A STACK; (B) EXTENDING A FLANGED METAL MEMBER ALONG SAID STACK WITH THE FLANGE THEREOF ENGAGING ONE END OF THE STACK, SAID METAL MEMBER HAVING A THERMAL COEFFICIENT OF EXPANSION SUBSTANTIALLY HIGHER THAN SAID INSULATING MEMBERS; (C) POSITIONING A SECOND METAL FLANGE IN ENGAGEMENT WITH THE OTHER END OF SAID STACK; (D) HEATING THE ASSEMBLY TO A TEMPERATURE OF AT LEAST 800*C., TO CAUSE SAID METAL MEMBER TO EXPAND THERMALLY SUBSTANTIALLY MORE THAN SAID STACK, AND THEN ATTACHING SAID SECOND FLANGE TO SAID METAL MEMBER AT SAID TEMPERATURE WHILE EXERTING PRESSURE ON SAID STACK THROUGH SAID FLANGES. 